Well-organized CN-M/CN-U/Pt-TiO2 ternary heterojunction design for boosting photocatalytic H2 production via electronic continuous and directional transmission

Abstract

Developing highly efficient heterojunction photocatalysts, especially ternary heterojunctions, is a promising strategy to enhance hydrogen (H2) production activity in the photocatalytic process. The compatibility of components and the matching of electronic structure are main challenges in constructing novel photocatalytic activity ternary heterojunctions which include sufficient light absorption, controlled electronic transmission, and high electron utilization efficiency. In this research, the electronic structure of carbon nitride (CN) was regulated continuously by selecting different nitrogen-rich precursors and changing calcination methods, and then CN/CN isotype heterojunctions were constructed to improve the compatibility of components. Next the CN/CN isotype heterojunctions were composited with Pt–TiO2 to design and construct different models of ternary heterojunctions successfully. The different effects of components alignment, band structure and light absorption on photoelectrical and photocatalytic activities were studied systematically in ternary heterojunctions. Among them, the efficient melamine-derived carbon nitride (CN-M)/urea-derived carbon nitride (CN-U)/Pt-TiO2 (CN-M/CN-U/Pt-TiO2) ternary heterojunction has outstanding photocatalytic activity in which the H2 production rate reaches a maximum of approximately 1735 μmol h−1 g−1 using triethanolamine (TEOA) as the sacrificial reagent under visible light irradiation. The H2 production rate is about 4.9 times that of the pure CN-U component, 2.2 times that of the CN-M/CN-U isotype heterojunction and 3.5 times that of the CN-U/Pt-TiO2 binary heterojunction. By means of high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), fluorescence emission spectra, photoelectrochemical and other measurements, the outstanding performance attributed to the well compatible and composited sequence of components, rational energy level alignment and favorable band offset. It is confirmed to result in sufficient light absorption, high efficiency of photo-induced charge separation, and efficient electronic continuous and directional transmission (prolonging the electron lifetime).The study took advantage of the controllability of the electron structure in CN photocatalyst, and provides a facile approach to designing highly efficient visible light responding CN-based ternary heterojunctions for multi-functional applications in the photocatalytic research field.